1. Field of the Invention
This invention relates to flowpath liners through gas turbine engine frames and, more particularly, to using hangers to mount such liners to casings having hooks.
2. Description of Related Art
A gas turbine engine of the turbofan type generally includes a forward fan and booster compressor, a middle core engine, and an aft low pressure power turbine. The core engine includes a high pressure compressor, a combustor, and a high pressure turbine in a serial flow relationship. The high pressure compressor and high pressure turbine of the core engine are interconnected by a high pressure shaft to from the high pressure rotor. The high pressure compressor is rotatably driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in the combustor and ignited to form a high energy gas stream. The gas stream flows aft and passes through the high pressure turbine, rotatably driving it and the high pressure shaft which, in turn, rotatably drives the compressor.
The gas stream leaving the high pressure turbine is expanded through a second or low pressure turbine. The low pressure turbine rotatably drives the fan and booster compressor via a low pressure shaft, all of which form the low pressure rotor. The low pressure shaft extends through the high pressure rotor. Most of the thrust produced is generated by the fan. Engine frames are used to support and carry the bearings which, in turn, rotatably support the rotors. Conventional turbofan engines have a fan frame, a mid-frame, and an aft turbine frame. Bearing supporting frames are heavy and add weight, length, and cost to the engine.
The mid-frame typically has an external casing and an internal hub which are attached to each other through a plurality of multiple radially extending struts. A flowpath frame liner provides a flowpath that guides and directs hot engine gases through the frame and is not intended to carry any structural loads. The flowpath frame liner includes a radially outer liner, a radially inner liner, and multiple fairings disposed between the outer and inner liners. In some gas turbine engines, the frame liner is segmented and fairing segments have hollow airfoils extending between radially inner and outer band segments. Radially inner and outer liner segments are circumferentially disposed between the inner and outer band segments, respectively.
The flowpath frame liner protects the struts and rest of the frame from the hot gases passing through the frame. Attaching the flowpath liner to the external casing of the frame has always been a challenge to engine designers. The flowpath liner is exposed to the hot engine gases whereas the casing is not. This presents a thermal mismatch between the casing and flowpath liner during engine transients. The attachment of the flowpath liner to the casing must accommodate differential thermal growth between the casing and flowpath liner. One current design for attaching the flowpath liners to the casing includes the use of a plurality of hangers. The hangers are attached between the casing and the flowpath liners in such a way as to support the liners and allow them to move relative to the casing to accommodate the differential thermal growth between the casing and flowpath liner. The outer liners and the fairings are separate segments. There are forward and aft hangers.
The aft hangers are bolted to the casing and the liner and fairing segments. Axially extending joints circumferentially disposed between the hangers and the liner and fairing segments allow for relative movement along the direction of mating surfaces. The forward hangers are bolted to hooks in the casing and in the liner and fairing segments. The forward hangers have circumferentially spaced apart tabs that protrude axially forward and these tabs are disposed through slots cut in a forward casing ring. A typical hanger may have three tabs and a C-clip is press fit onto the tabs and secure the hangers to the forward casing ring. One of the tabs has a longer axial length than the other two and protrudes through a slot in the C-clip to prevent rotation of the C-clip. The added length may be in the form of a pin instead the entire width of the tab being longer.
It is desirable to have a lower cost, lighter weight, and more durable and robust support means to attach the flowpath liner to the casing. It is desirable to have a support means that reduces assembly and disassembly time as compared to present designs. The C-clips are subject to cracking and are frequently replaced during engine overhaul and, thus, a more durable and robust support means is desired.
An annular hanger for supporting an annular wall element from a gas turbine engine annular outer casing. The annular hanger having an annular body section circumscribed about a centerline extending in opposite first and second axial directions, an annular first hook extending in the first axial direction from said body section, and an annular second hook extending in the second axial direction, opposite that of said first axial direction, from the body section. One of the hooks has circumferentially spaced apart hanger tabs, such as three in the exemplary embodiment, extending equal axial lengths from the body section and a corresponding number of notches wherein each of the notches is circumferentially disposed between a corresponding adjacent pair of the hanger tabs.
In the exemplary embodiment of the invention illustrated herein, the first hook includes the tabs and the annular hanger further comprises a third annular hook extending in the second axial direction from the body section. The second and third annular hooks extend in the second axial direction from said body section and the third annular hook is located radially inwardly of the second annular hook. The first hook includes the hanger tabs and the annular hanger further includes a third annular hook extending in said second axial direction from said body section.
The invention also includes a gas turbine engine frame liner assembly with an annular outer casing, an annular wall element mounted to and spaced radially inwardly of the outer casing, and the annular hanger supporting at least in part the wall element from the outer casing. The circumferentially spaced apart hanger tabs is part of a bayonet mount supporting at least in part the wall element from the outer casing. The bayonet mount further includes a bayonet slot on one of the casing and the wall element and the hanger tabs are received within the bayonet slot. The bayonet slot is bounded by an annular bayonet hook having a plurality of circumferentially spaced apart bayonet tabs and a corresponding plurality of bayonet spaces, each of which is circumferentially disposed between each pair of the bayonet tabs.
The invention also includes a gas turbine engine frame assembly having a frame with the annular outer casing and an annular inner hub circumscribed about the centerline and spaced radially inwardly from the casing. A plurality of circumferentially spaced apart hollow struts extending radially between the outer casing and the hub and a circumferentially disposed plurality of the annular wall elements are mounted to and spaced radially inwardly of the outer casing supported by a circumferentially disposed plurality of the annular hangers. In a more particular embodiment of the invention, the wall elements are circumferentially alternating outer liner segments and outer fairing platforms of fairing segments.
The hangers and bayonet mounts of the present invention provide a lower cost, lighter weight, and more durable and robust support means to attach wall elements to a gas turbine engine casing. The bayonet mount of the present invention can also reduce assembly and disassembly time as compared to present designs. The present invention eliminates C-clips and cracking and frequent replacement of the C-clips during engine overhaul and provides a more durable and robust support means.